High frequency transmission apparatus



March 26, 1935. GEBHARD 1,995,301

HIGH FREQUENCY TRANSMISSION APPARATUS Filed March 14, 1933 2Sheets-Sheet l INVENTOR. QOMZ/J a. 9456M Ai EORNZ Patented Mar. 26, 1935UNITED STATES PATENT OFFICE HIGH FREQUENCY TRANSMISSION APPARATUS LouisA. Gebhard, Washington, D. 0.

Application March 14,

12 Claims.

1933, Serial No. 660,705

. My invention relates broadly to radio transmission systems and moreparticularly to an arrangement of high frequency inductance system forradio transmission systems.

One of the objects of my'invention is to provide an improvedconstruction of adjustable inductance system for high frequencytransmission systems.

Another object of my invention is to provide a high frequencytransmission circuit in which frequency adjustments may be made byvariation of inductance in the high frequency circuit instead ofcapacity change, for maintaining distributed capacity in the circuit ata minimum.

Still another object of my invention is to provide a construction offluid cooled inductance system having means for selectively tuning theinductance system to desired frequencies.

A further object of my invention is to provide means for tuning a fluidcooled inductance system by selectively shunting portions of the turnsof the inductance while circulating cooling fluid through the entirelength of the turns of the inductance.

A still further object of my invention is to provide a construction ofan improved inductance system for a push-pull high power high frequencyamplifier system, wherein the electrical center of the inductance isfixed at the geometrical center thereof coincident with the inlet anddischarge of cooling fluid in concentric paths through the inductancefor reducing electrical losses to a minimum.

Other and further objects of my invention reside in a construction ofselectively adjustable inductance system as set forth more fully in thespecification hereinafter following by reference to the accompanyingdrawings wherein:

Figure 1 is a side elevation of a portion of a high frequencytransmitter constructed in accordance with my invention and showing theinductance system of my invention; Fig. 2 is a horizontal sectional viewtaken on line 22 of Fig. 1; Fig. 3 is a horizontal sectional view takenon line 3-3 of Fig. 1; Fig. 4 is a transverse vertical sectional viewtaken on line 4-4 of Fig. 1; Fig. 5 is a transverse vertical sectionalview taken on line 5-5 of Fig. 1; Fig. 6 is a schematic diagram of apush-pull amplifier embodying my invention employed in the type of highfrequency transmitter shown in the foregoing views; and Fig. 7 is aperspective view showing the arrangement of the inner cooling coils inthe inductance system of my invention.

In a high frequency transmitter covering a wide frequency band, it isdesirable to have as high a L/C ratio as possible in the output circuit.A high L/C ratio will result in maximum reactance of the circuit withminimum current in it.

Minimum current will also result in minimum 5 loss in the inductorsforming the circuit. In a high power transmitter employing liquid cooledtubes, it is desirable to introduce the cooling liquid into the systemat a low radio frequency potential point. This point exists in apushpull system near the geometric center of the coil system. Bydesigning the coil so that it will have dual liquid cooling paths with asingle electrical path, it is possible to pass the cooling fluid up tothe tubes and return without incurring excessive losses through themedium of the cooling fluid. It is possible to obtain a greaterfrequency range in any transmitter by utilizing inductance variationthan is possible by using capacity variation. This is due to the factthat the distributed capacities in the circuit are considerable, and itis impossible to reduce the total cap ity of the circuit beyond thedistributed capacity of the inductance. It is possible, however, to sodesign the system, that the inductance remaining in the system at theminimum point, is very small.

The inductance consists of a number of rectangularly shaped turns 1,formed of a compound coil connected between the liquid cooling jacketssupporting the two electron tubes of the pushpull system. The conductorof the coil is formed by the compound tube which comprises two tubes, anouter tube 2, and an inner tube 3. At the geometric center of the coil,these tubes are tapped as shown at 4, to permit the cooling liquid to beintroduced and discharged. The coil 1 is supported by insulating members5 and 6 from the framework 7 and 8 of the transmitter. The variation ofinductance is obtained through the movement of short circuiting bars 9mounted on each of the turns. Connection to each vertical member formingthe turn, is made from the short circuiting bar by means of cylindricalbrushes 10. The group of short circuiting bars is mounted on insulatingmember 11, which is caused to move by means of screws 12 and 13, drivensimultaneously through gears from a control 14 mounted on the frontpanel of the transmitter. An indicating mechanism 15 connected throughgears with the control 14 is provided to show the position of the shortcircuiting bar.

With the short circuiting bars in the extreme upper position, the totalinductance in the circuit is cut out with the exception of the shortlength between the tubes. With the short circuiting bars in the extremelower position, all the inductance is connected in the circuit.Intermediate positions provide intermediate values of inductance. Itshould be noted that the short circuited portions of the coil are not inthe extremely intense part of the magnetic field of the system,therefore, the currents set up in them are low. This means that thelosses in this part of the system are not excessive. By arranging shortcircuiting bars on each individual turn, the natural period of the shortcircuited loop is at an extremely high frequency far beyond thefrequency of response of the complete system. Therefore, the resonanteffects are remote and the possibility of setting up large currents dueto these effects is a minimum.

Referring to Figure 6 of the drawings, I have shown the inductancesystem of my invention applied to a push-pull amplifier constituted byelectron tubes 20 and 21. The tubes 20 and 21 are the high power fluidcooled tubes illustrated in Figs. 1, 4 and 5. Tube 20 includes cathode20a, control grid 20b, and anode 20c. Tube 21 includes cathode 21a,control grid 21b and anode 21c. Cathodes 20a and 2111 are energized fromtransformer system 22 operating from an alternating current supplycircuit 23. The input system for the electron tubes connects through theinductively coupled transformer system 24 connected in symmetricalrelation to the control grids 20b and 21b. The output circuit of the twotubes is connected through the dual conductor fluid cooled inductance 1as shown. The adjustable short-circuiting bars 9 have beendiagrammatically illustrated in Fig. 6. The fluid is introduced anddischarged in the dual conductor inductance centrally of the inductanceat 4. The point at which the fluid enters and is discharged from theinductance 1 is connected to ground 25 through condenser 26 forestablishing the electrical center of the coil at the geometric centerof the coil and eliminating high frequency losses due to any disturbanceof symmetry in the circuit. This path to ground is extremelyshort'andofiers a low impedance to the passage of high frequencycurrents. The high potential for the output circuit of tubes 20 and 21is supplied to the tubes at the geometric center of the inductance 1from terminals 27 shunted by radio frequency bypass condenser 28. Asuitable negative potential is applied to the control grid electrodesfrom a source connected at 29 with bypass condenser 30 connected inshunt thereto. Sets of bypass condensers 31 and 32 are connected in thecathode circuits. Balancing condensers 33 and 34 are connected betweenthe output circuit of one tube and the input circuit of thesymmetrically arranged adjacent tube. Coupling condensers 35 and 36 areconnected between inductance 1 and the circuit to which power isdelivered from the symmetrically arranged electron tube system asrepresented by terminals 37. It will be observed that the tuning of theoutput circuits of the adjacent tubes is effected by adjustment of theshort-circuiting bars 9 for rendering selected amounts of the inductance1 effective.

The extremely short leads which are necessary between the electrodes ofthe electron tube and the inductance system insures a high degree ofemciency in the transmitting apparatus of my invention. The fact that itis unnecessary to effect a capacity change for tuning the apparapurposeswithout the payment of any royalty I thereon or therefor.

What I-claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. High frequency signaling apparatus comprising an inductance, andmeans for varying said inductance comprising means for simultaneouslyshunting a portion of each turn of said inductance.

2. High frequency signaling apparatus comprising an inductance havingthe turns thereof wound in substantially rectangular contour, slidablecontact members electrically connected together in pairs, the members ofa pair engaging parallel extending portions of a turn of saidinductance, and means for simultaneously controlling the movement ofsaid contact members for variably shunting portions of each of the turnsof said inductance simultaneously.

3. A high frequency inductance system comprising a tubular winding withthe opposite sides of each turn thereof formed in substantiallyrectangular contour, electrically conductive slidable bridge membersdisposed between said opposite sides of each turn, and means forsimultaneously adjusting the position of said electrically conductiveslidable bridge members for electrically shunting portions of each ofthe turns of the said inductance.

4. A high frequency inductance system comprising a tubular element woundin a substantiallyrectangular contour with opposite sides of each turnextending parallel, electrically conductive slidable bridge membersinterconnecting the opposite sides of each turn, and means forsimultaneously adjusting the position of said electrically conductiveslidable bridge members with respect to each of said turns forelectrically shunting in variable amounts'each of the turns constitutingsaid inductance.

5. A high frequency inductance comprising a conductor wound in asubstantially rectangular contour, each of said turns having oppositesides extending parallel to each other, an electrically conductiveslidable bridge member extending between the opposite sides of each ofsaid turns,

and means for simultaneously adjusting the position of the saidelectrically conductive bridge members along each of the turns of saidinductance for adjustably controlling the effective electrical paththrough the said inductance.

6. A high frequency inductance comprising a conductor wound in asubstantially rectangular contour, each of said turns having oppositesides extending parallel to each other, an electrically conductiveslidable bridge member extending between the opposite sides of each ofsaid turns, and means at each end of said inductance for simultanouslycontrolling the adjustment of each of said bridge members along theopposite sides of each of the turns of the said inductance forsimultaneously controlling the effective electrical path through saidinductance.

'7. A high frequency inductance system comprising a conductive twintubular member providing a dual path for cooling fluid and a single pathfor electrical energy, said tubular member wound in a substantiallyrectangular contour with opposite sides or each turn extendingsubstantially parallel to each other, fluid inlet and dischargeconnections disposed centrally of said tubular inductance, andelectrically conductive slidable bridge members extending between theopposite sides of each of the turns of the said inductance, an insulatedmember interconnecting said electrically conductive slidable bridgemembers, and means engaging said insulation member at each end of saidinductance for simultaneously advancing or retracting the saidinsulation member for correspondingly controlling the position of saidelectrically conductive slidable bridge members with respect to theturnsof said inductance for simultaneously shunting out portions of each ofthe turns of said inductance.

8. A high frequency inductance system comprising -a tubular member woundin a coil of substantially rectangular contour and having opposite sidesof each turn extending parallel one to the other, a rotary screw feedmember located adjacent each end of said inductance and in a pathsubstantially parallel to the plane of the turns of the said inductance,means for simultaneously driving each of said screw feed members, acarrier mounted between said screw feed members and adjustable tovarious positions normal to the planes of the turns of said inductance,bridge members extending between the parallel extending turns of thesaid inductance and connected with said carrier for adjustably shuntingportions of the turns of said inductance in accordance with theselectivemovement of said carrier.

9. High frequency signaling apparatus comprising an inductance havingits turns disposed coaxially in substantially parallel planes, saidinductance comprising means providing a dual path for cooling fluid anda single path for electrical energy, means for introducing anddischarging cooling fluid substantially at the center of saidinductance, and means for variably and simultaneously shunting portionsoi each 01' the turns of said inductance for selectively controlling theefiective value of inductance.

10. High frequency signaling apparatus comprising an inductance havingits turns disposed coaxially in substantially parallel planes, saidinductance comprising means providing a dual path for cooling fluid anda single path for electrical energy, means for introducing anddischarging cooling fluid substantially at the center of saidinductance, means for variably and simultaneously shunting portions ofeach of the turns of said inductance for selectively controlling theeffective value of said inductance, and means connected with saidinductance at the fluid inlet and discharge central connection; theretofor fixing the electrical center of the said inductance at the saidcentral fluid inlet and discharge connections whereby the electricalcenter of said inductance is maintained in position independent of thechange in position of said shunting means.

11. A high frequency inductance comprising a conductor wound in apolygonal contour, an electrically conductive slidable bridge memberextending parallel to one side of said polygonally wound inductance andcontacting opposite points on each of the turns of said inductance, andmeans for simultaneously adjusting the position of the said electricallyconductive bridge members along each of the turns of said inducance foradjustably controlling the inductive reactance of said inductance.

12. A high frequency inductance comprising a conductor wound insubstantially rectangular contour, an electrically conductive slidablebridge member extending across opposite sides of each of the turns ofsaid inductance, and means for simultaneously adjusting the position ofthe said electrically conductive bridge members on each of the turns ofsaid inductance for effecting nonlinear variation of the inductivereactance of said inductance with respect to the movement of saidconductive bridge member.

LOUIS GEBHARD

